Based on the history of four groups of mood adverbs, namely the fanzheng反正group, the bijing畢竟group, you又, and ye 也, this paper argues that grammaticalization can be triggered by the ellipsis and compacting of complex sentences. The fanzheng and bijing groups of mood adverbs were originally equal to concessive clauses and constructed concessive relations with the sentences they occurred, while you and ye were adversative adverbs and experienced the ellipsis of the previous sentence. These two types of developments all contain the ellipsis and compacting of complex sentences, either from complex sentences to simple sentences or from partially overlapped complex sentences to general complex sentences. Their histories demonstrate not only the flexible transformation between simple sentences and complex sentences in Mandarin Chinese, but also the complex properties of these mood adverbs.